1. Field of the Invention
This invention relates to a novel optical element, and more particularly, to an optical element utilizing the light scattering property of gel.
2. Description of the Related Art
As office automation (OA) has recently been developed, display devices have been widely used in the field of business machine. Desirable display devices are those which do not cause fatigue of eyes even when used for a long time. Heretofore, as the display element, there have been known non-luminant type display elements such as electric field coloring devices (ECD), liquid crystal devices (LCD) and the like.
However, there are disadvantages that ECD has a low display contrast and LCD has a narrow visual field angle. When these devices are used as light modulation elements such as light shutter and the like, there are the same disadvantages.
Heretofore, there has been widely effected recording or display by using light flux. A technique for modulating the light flux is disclosed, for example, in Japanese Patent Application Laid-open No. 56-5523, that is, modulation of light is conducted by changing the electric field in the crystal having an electrochemical effect and diffracting light flux incident on the part where the refractive index in crystal is changed by the distribution of electric field.
On the other hand, distribution of refractive index due to thermal effect is utilized to modulate light. The light modulation of this type is disclosed in "Deflection of light by change of refractive index due to heat" (NIKKEI ELECTRONICS, issue of Aug. 16, 1982) or "Response speed of TO glass wave guide type light switch" (Denshi Tsushin Gakkai, General national meeting, 1982).
However, electrochemical crystal of the conventional techniques is expensive and it is necessary upon using the crystal to give a predetermined characteristics to a light flux incident on the crystal. When modulation of light is effected, there is a restriction that light flux should be incident parallel to the electrode as far as possible so as to cause total reflection of the light flux at the portion in an optical crystal material where the electric field distribution is generated and improve the diffraction efficiency.
On the other hand, according to the method utilizing thermal effect, a TiO.sub.2 crystal or a glass produced by an ion exchange method is used as a thermal effect medium. In general, dependency of refractive index of solid on temperature is so low that voltage applied across electrodes or voltage applied to a heater resistance should be high so as to obtain a desired deflection characteristics.
In the examples as above, the propagation device of the incident light flux is limited with respect to the position of electrode and heater so as to obtain a deflection characteristic of good efficiency. As mentioned above, since the temperature dependency of refractive index is small, it is necessary to propagate the light flux at a region near to the electrode and heater as far as possible and parallel to the electrode and heater surface so as to give an appropriate phase change.
In conventional display elements, for example. ECD, there are drawbacks that display contrast is low, image surface is not seen easily, and in case of LCD, the visual field angle is narrow. Therefore, none of them can not sufficiently meet the demand that fatigue of eye of the user is not caused even if the device is used for a long time. These conventional display elements can be utilized as a light modulation element such as light shutter and the like, and also suffur from the similar drawbacks.